As most people know, Benjamin Franklin had numerous inventions that ranged from small convienences to incredible things that changed how people lived. The bifocals didn’t necassarily change how people lived, but they were more than a small improvement for anyone who had multiple sets of glasses to wear.
He is credited with the invention somewhere in the 1960’s, with the first evidence of them coming in a 1964 political cartoon. His first reference to his double spectacles came in a letter in 1984, quite a few years after the original invention.
His original design had the more convex lens placed on the bottom of the glasses (close viewing), while the lesser convex lens was placed on the upper half. Originally the lens’s were actually 2 seperate ones put into the same frame – it wasn’t until the 20th century that lenses were fused together to create bifocals.
While the bifocals are a great convienence for many, they are known to cause dizziness and headaches because of the differing perspectives. This is similar to how you may feel after wearing glasses that aren’t your prescription for an extended period of time.
By their very nature, bifocals offer a limited field of vision for the differeing distances. This can cause wearers to move reading material instead of their heads when reading, to make sure that what they are reading stays in the correct perspective.
This is just one of the examples of how Ben Franklin took a problem that people had, and found a solution.